Current vehicles utilize accessory drive systems to supply power to vehicle accessories (e.g., air conditioner systems, power steering systems, power braking, alternators, and pumps (e.g., oil, coolant and the like). The accessory drive system includes a belt coupled to the engine through one or more pulleys. A problem associated with current vehicles is that power is not transferred to the accessories as efficiently as desired. Current accessory drive systems deliver sufficient power to operate accessories over the entire range of the engine's operational speeds. Engines can operate at speeds from, for example, 500 RPM (revolutions per minute) to 8000 RPM, and the pulleys of the accessory drive systems operate at speeds that are directly proportional to the engine speed. In order to deliver sufficient power to the vehicle accessories over the entire range of operational engine speeds, a fixed ratio of engine speed to accessory drive system pulley speed is selected such that the accessory drive system can distribute sufficient power to operate the accessories at the lowest engine speeds. However, by selecting the ratio so that the engine supplies sufficient power to operate the accessories at the lowest engine speeds, the engine is configured to supply excess power to the accessories at higher engine speeds, and the excess energy is thereby dissipated by the vehicle.
In current hybrid vehicles, the engine shuts down under selected conditions (e.g., when the vehicle is braking or when the vehicle is at rest) to reduce the engine's fuel consumption. The hybrid vehicles utilize electric motors to power accessories when the engine is shut down. A problem associated with current hybrid vehicles is that the electric motors utilized to power the accessories under all operating conditions. This is inefficient because of the low round-trip efficiency of converting mechanical energy from the engine to electrical energy, storing the electrical energy in the battery as chemical energy, converting the chemical energy from the battery to electrical energy then back to mechanical energy to drive the accessories. Additionally, this approach increases the vehicle costs over vehicles having power distribution systems that power accessories by directly transferring rotational power generated by the engine.
Therefore, a power distribution system that can more efficiently distribute power to vehicle accessories and can reduce vehicle costs is needed.